In order to statically balance a rotor, i.e. to position the center of gravity of the rotor on the axis of rotation, it is a common practice to support the rotor on a pivot disposed above the center of gravity of the rotor and located on the axis of rotation of the rotor. Means such as a spirit level is used to indicate the angle which the axis of rotation makes with the vertical when the rotor comes to rest. Weights are then added to the rotor until the axis of rotation of the rotor lies in the vertical direction.
For use in balancing the wheels of automotive vehicles, the so-called bubble balancers are most commonly used. Such balancers generally employ a ball and platen to provide the pivot point about which the rotor being balanced freely pivots. While such ball and platen pivot assemblies can be satisfactorily used to balance these types of wheels they do not function well with the large massive rotors used in heavy industry. There are two principal reasons for this. One reason is that the extremely high pressure occurring at the pivot point causes the ball surface to flatten, or if the ball is harder than the platen, the platen surface becomes indented. In either case, the enlarged contact area between the ball and the platen reduces the sensitivity of the balancer. The second reason is that the high pressure on the ball will, in many instances, actually crush the ball. As a consequence, large rotors cannot be balanced with the bubble balancers of the prior art.
Another type of rotor balancer utilizes a relatively long wire or tension member to hang the rotor from a support. Such balancers are difficult to read with any degree of accuracy and, of course, they cannot be used with large industrial type rotors because of the limitation in the tensile strength of the wire.
In addition to the need for a balancer for use with large heavy rotors there is also a need for a balancer which can be used to balance relatively small rotors such, for example, as circular saw blades. While I have used the usual ball and platen pivot assemblies to improve the balance of such blades, the balance condition thus achieved is not sufficiently accurate to eliminate all noticable vibration when such blades are rotated at the normal speeds.